Re: Feature Proposal: Connection Pool Optimization - Change the Connection User

Hi Jacob and Daniel,

Thanks for your feedback.

>@Daniel - I think thats conflating session_user and current_user, SET ROLE is not a login event. This is by design and discussed in the documentation..

Agreed, I am using those terms loosely. I have updated option 4 in the proposal document. I have crossed it out. Option 5 is more suitable "SET SESSION AUTHORIZATION" for further consideration.

>@Daniel - but it's important to remember that we need to cover the functionality in terms of *tests* first, performance benchmarking is another concern.

For implementation absolutely, but not for a basic feasibility prototype. A quick non-secure non-reliable prototype is probably an important first-step to confirming which options work best for the stated goals. Importantly, if the improvement is only 5% (whatever that might mean), then the project is probably not work starting. But I do expect that a benchmark will prove benefits that justify the resources to build the feature(s).

>@Jacob - A more modern approach might be to attach the authentication to the packet itself (e.g. cryptographically, with a MAC), if the goal is to enable per-statement authentication anyway. In theory that turns the middleware into a message passer instead of a confusable deputy. But it requires more complicated setup between the client and server.

I did consider this, but I ruled it out. I have now added it to the proposal document, and included two Issues. Please review and let me know whether I might be mistaken.

>@Jacob - Having protocol-level tests for bytes on the wire would not only help proposals like this but also get coverage for a huge number of edge cases. Magnus has added src/test/protocol for the server, written in Perl, in his PROXY proposal. And I've added a protocol suite for both the client and server, written in Python/pytest, in my OAuth proof of concept. I think something is badly needed in this area.

Thanks for highlighting this emerging work. I have noted this in the proposal in the Next Steps section.

--Todd

Note: Here is the proposal document link again - https://docs.google.com/document/d/1u6mVKEHfKtR80UrMLNYrp5D6cCSW1_arcTaZ9HcAKlw/edit#

On Tue, 23 Nov 2021 at 12:12, Jacob Champion <pchampion@vmware.com> wrote:

On Sat, 2021-11-20 at 16:16 -0500, Tom Lane wrote:
> One more point is that the proposed business about
>
> * ImpersonateDatabaseUser will either succeed silently (0-RTT), or
>   fail. Upon failure, no further commands will be processed until
>   ImpersonateDatabaseUser succeeds.
>
> seems to require adding a huge amount of complication on the server side,
> and complication in the protocol spec itself, to save a rather minimal
> amount of complication in the middleware.  Why can't we just say that
> a failed "impersonate" command leaves the session in the same state
> as before, and it's up to the pooler to do something about it?  We are
> in any case trusting the pooler not to send commands from user A to
> a session logged in as user B.

When combined with the 0-RTT goal, I think a silent ignore would just
invite more security problems. Todd is effectively proposing packet
pipelining, so the pipeline has to fail shut.

A more modern approach might be to attach the authentication to the
packet itself (e.g. cryptographically, with a MAC), if the goal is to
enable per-statement authentication anyway. In theory that turns the
middleware into a message passer instead of a confusable deputy. But it
requires more complicated setup between the client and server.

> PS: I wonder how we test such a feature meaningfully without
> incorporating a pooler right into the Postgres tree.  I don't
> want to do that, for sure.

Having protocol-level tests for bytes on the wire would not only help
proposals like this but also get coverage for a huge number of edge
cases. Magnus has added src/test/protocol for the server, written in
Perl, in his PROXY proposal. And I've added a protocol suite for both
the client and server, written in Python/pytest, in my OAuth proof of
concept. I think something is badly needed in this area.

--Jacob

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Todd Hubers